It is believed that twisting and bending exercises of the body can be of therapeutic effect to tone, strengthen, loosen and otherwise provide a health benefit to various parts of the body, including the legs, arms, shoulders, hips and, specifically, to the lower torso. By lower torso, what is meant is the lower back, including the spine and muscle groups, such as erector spinal, gluteus medius, illiac crest and lower abdomen, including the muscle groups of rectus abdominis, obliquus externus abdominis and connected ligaments. Twisting and bending of the upper body about the longitudinal axis, i.e., the axis extending from the top of the head through the body to the ground, has particular effect on the aforesaid muscles, ligaments and the spine. The longitudinal axis is contained in the median sagittal plane of the body which bisects the body front to back. This twisting or bending exercise may be for general health and muscle toning, or may be rehabilitative in nature to relieve back pain or to strengthen the back after an injury thereto.
One device according to the prior art which can be used by a twisting motion is disclosed in Dantolan, U.S. Pat. No. 2,528,213, issued Oct. 31, 1950. The device according to this reference is in the nature of a bar bell, including hand grips at each end of a member. A weight is slidably disposed on the member, spring cushions being provided at the handles to cushion the weight upon engagement thereof. To use the device in a twisting motion, the device is held at arm's length and the body is twisted. The weight moves back and forth between the handles being cushioned each time it engages a spring.
A drawback of this type of device is that often unusual strain on the back and shoulder muscles is imposed since the person must hold the device a distance away from the body, preferably at arm's length, so that the sliding weight may freely move. Since the muscles of the lower back are used to so position the device, these muscles are tensed which tends to prevent full twisting of the upper torso. Furthermore, the muscles of the shoulders and back may tire before a full therapeutic effect can be delivered to the lower torso. Additionally, since the device is held away from the body, the shoulders and arms may tend to move without inducing the desired full twisting of the lower torso. Full twisting is believed to be beneficial as both an exercise and to loosen or limber up the lower back and abdomen. As an added drawback, the springs of the Dantolan device act to absorb the momentum imparted to the traversing weight by the twisting motion and, hence, devices of this kind fail to take full advantage of that momentum to induce full twisting of the torso.